近年來隨著通訊技術的進步, 錯誤更正碼被廣泛地運用在通訊系統上面, 而低密度奇偶檢查碼(LDPC) 更是在新一代的無線通訊系統上被大量運用並且納入規格中。在這篇論文中, 我們提出一些方法來改善數位廣播-第二代衛星通訊系統(DVBS2)的效能。由於數位廣播-第二代衛星通訊系統中低密度奇偶檢查碼解碼器的硬體面積過大, 我們提出一種動態量化的量化方式, 得以在解碼效能不損失的情況下, 減
少外部資訊值(Extrinsic message) 的量化位元數, 以減少硬體實現的面積。我們基於外部資訊值的絕對值會有越來越大的趨勢, 故在疊代次數不同的情形下, 採用不同的量化方式。如此一來, 可以得到較好的解碼效能, 甚至可以達到節省硬體的效果。此外, 我們根據低密度奇偶檢查解碼器使用OMS 演算法解碼的特性, 發現次小的訊息節點連接到檢查節點的外部資訊值對於碼率高的低密度奇偶檢查解碼器更新檢查節點連接到訊息節點的外部資訊值來說, 影響甚小。因此我們可以減少其儲存位元, 並在讀取時加入適當的補償。這樣一來, 則可以在解碼效能不損失的情況下達到節省硬體面積的效果。另一方面, 我們利用信號調變上的特性來提供一種選擇性映射的方法, 以降低信號傳送的能量。而在相同訊雜比(SNR) 的情況下可以得到較好的位元錯誤率(BER), 抑或是在信號使用較低能量傳輸時不會有解碼效能的損失。然而, 這個方法也易於硬體實現上面。

In this thesis, we propose an adaptive quantization to reduce the number of quantization bits of extrinsic values. We can use different quantization schemes at different iteration numbers in order to achieve better error performance. In addition, we can reduce the storage of the second minimum of extrinsic message in an LDPC decoder using OMS algorithm, since this second minimum has little effect on the error performance of high-rate LDPC decoders. Finally, we also try to reduce transmitted codeword energy for DVB-S2 system by selective mapping without degradation in error performance.

摘要 I
誌謝 II
目錄IV
內文目錄 V
圖目錄 VII
表目錄IX
第一章緒論 1
第二章低密度奇偶檢查碼的回顧 3
第三章EXIT Charts 的回顧 11
第四章動態量化17
第五章節省記憶體的存取方式 46
第六章選擇性映射50
第七章結論 55

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